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CORROSION AND PRESERVATION 


OF IRON AND STEEL 



CORROSION AND PRESERVATION 
OF IRON AND STEEL 



FIRST EDITION 



By 

ARMAND J. P. VANDERMYN 





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Cdpjfh^h + Office 

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m 2 1928 


2 9-/2 n 4 2 


DEDICATION 


TO THOSE WHO HAVE IN THE PAST, 

AND TO ALL THOSE WHO 

WILL IN THE FUTURE, CONTRIBUTE TO PROGRESS 
IN GENERAL AND THE PRESERVATION OF 
IRON AND STEEL IN PARTICULAR, 

THIS BOOK IS RESPECTFULLY 
DEDICATED 



CONTENTS 

r 

PAGE 


INTRODUCTION. 11 

Chapter I Why Iron and Steel Should Be Protected . 13 

Chapter II The Electrolytic Theory of Corrosion . 19 

Chapter III Prevention of Corrosion. 32 

Chapter IV Stimulative and Inhibitive Pigments . . 47 

Chapter V The Law of Maximum and Minimum Voids . 61 
Chapter VI Protection Against the Action of Sea Water 67 
Chapter VII Concrete as a Protector Against Corrosion 70 





INTRODUCTION 


C HE protection against corrosion of iron and 
steel is a problem to which has been given 
more thought and study in the past five years 
than in the previous five hundred years. Many 
eminent authorities have conducted their investi¬ 
gations both from a practical and theoretical point 
of view, and the conclusions arrived upon have 
the support of many practical men. 

The writer has conducted a number of experi¬ 
ments and while in some instances it was difficult 
to absolutely determine the influence which elec¬ 
tricity brings to bear upon the corrosion problem, 
enough evidence has been secured to accept the 
electrolytic theory of corrosion as the correct one. 
It is the aim of the writer to discuss in this 
booklet the electrolytic theory of corrosion and 
present for your consideration an outline of 
the cause and prevention of the most 
insidious enemy of iron—Rust. 


Pittsburgh 
October 1st, 1921 




CORROSION AND PRESERVATION 
OF IRON AND STEEL 

r 

Chapter I 

Why Iron and Steel Should be Protected 

T is not within the power of any man 
to predict the future, and to say in 
these days of progress, substitution 
and discovery that our supply of 
iron ore will become exhausted, is 
perhaps saying too much. Nothing, however, can 
be gained by ignoring facts. 

When we consider that the annual production of 
pig iron in the United States alone grew from about 
14,000,000 tons in 1900 to about 55,000,000 tons in 
1920, one may well ask, “ How long will the world’s 
ore supply stand the drain upon it?” Enormous 
quantities of the finished product are allowed to 

—page thirteen 














CORROSION AND PRESERVATION OF IRON AND STEEL 


perish yearly for lack of adequate protection, and 
unless civilization learns to protect and preserve 
its stores of iron and steel already manufactured, 
future generations may be compelled to find either 
a substitute for iron or develop a process by which 
non-corrodible iron can be manufactured. It is 
gratifying to observe that this important problem 
is receiving the thoughtful attention of many 
learned bodies, metallurgists and engineers, and 
while progress has been made in regard to manu¬ 
facturing iron and steel resistant to corrosion, the 
problem has by no means been solved, and until 
it has we must depend upon protective coatings. 

During the past twenty years the demand for 
steel has increased enormously not only in America 
but in the world. Last year’s exports of iron and 
steel products had a total value of $1,100,000,000, 
and in the same year more than 20,000,000 tons of 
pig iron were produced in the furnaces of England, 
France, Germany and Belgium. 

What the next twenty years will bring is of 
course a matter of conjecture, but it seems fair to 


— P a S. e fourteen 





WHY IRON AND STEEL SHOULD BE PROTECTED 


assume that the demand for steel will increase 
tremendously. 

Millions of tons of reinforcing steel will be used 
in the construction of the Nation’s highways, to 
say nothing of the immense tonnage of structural 
steel which will be fabricated into bridges crossing 
the rivers and Valleys over which these highways 
will run. 

Other millions of tons of structural steel will be 
required for the erection of modern fireproof sky¬ 
scrapers to house our ever-increasing population, 
to provide office buildings where the world’s busi¬ 
ness can be transacted, to build hotels, railroad 
terminals, factories, bridges, subways, ships—in 
fact, a thousand and one things necessary for 
modern civilization, and steel is the one product 
which can meet the demand. 

Can anyone imagine the plight of civilization if 
it were denied the utilization of steel? 

Can anyone advance reasons why we should not 
protect against corrosion every square foot of steel 
or iron produced? 


—page fifteen 




CORROSION AND PRESERVATION OF IRON AND STEEL 


Is there any reason why those who are devoting 
their time to the designing and creating of new 
steel structures should not take all precaution to 
see that the steel is properly protected against 
corrosion, and thus preserved? 

Is there any reason why those charged with the 
maintenance of steel structures should not be 
thoroughly conversant with the best possible means 
of protection? We think not. 

“A penny saved is a penny earned” is a saying 
with which all of us are acquainted, but not all of 
us realize that to preserve a ton of steel from 
destruction means not only a saving of the iron 
ore, but also the conservation of about four tons 
of coal. 

This point was forcibly brought out in Edwin E. 
Slosson’s book, “Creative Chemistry”, wherein he 
says, “Every year the blast furnaces of the world 
release 72,000,000 tons of iron from its oxides and 
every year a large part, said to be a quarter of that 
amount, reverts to its primeval forms. If so, then 
man after five thousand years of metallurgical 


—page sixteen 




WHY IRON AND STEEL SHOULD BE PROTECTED 


industry has barely got three years ahead of nature, 
and should he cease his efforts for a generation 
there would be little left to show that man had 
ever learned to extract iron from its ores. The 
old question, ‘What becomes of all the pins?’ may 
be as well asked of rails, pipes and threshing ma¬ 
chines. The end of all iron is the same. However 
many may be its metamorphoses while in the service 
of man, it relapses at last into its original state of 
oxidation. To save a pound of iron from corrosion 
is then as much benefit to the world as to produce 
another pound from the ore. In fact, it is of much 
greater benefit, for it takes four pounds of coal to 
produce one pound of steel, so when a piece of iron 
is allowed to oxidize it means that four times as 
much coal must be oxidized in order to replace it. 
And the beds of coal will be exhausted before the 
beds of iron ore. 

If we are ever to get ahead, if we are to gain any 
respite from this enormous waste of labor and 
natural resources, we must find ways of preventing 
the iron which we have obtained and fashioned into 
useful tools from being lost through oxidation.” 


—page seventeen 




CORROSION AND PRESERVATION OF IRON AND STEEL 


The aim of man is to create, to beautify and 
make permanent the fruits of his labor; then why 
should we spend large sums of money and years of 
work designing and erecting a steel structure,—be it 
a skyscraper, a manufacturing building, or a 
bridge,—only to allow the steel to revert back to 
that from which it was won—rust? 

Iron is the most useful of all metals. Its employ¬ 
ment in our everyday life is as necessary as is the 
food we eat. Without iron and coal, civilization 
would be in a sad plight, and it is reasonable to 
believe that man will realize the necessity of pro¬ 
tecting against destruction the world’s most valu¬ 
able product. 


—page eighteen 




THE ELECTROLYTIC THEORY OF CORROSION 


Chapter II 

The Electrolytic Theory of Corrosion 

Many experiments, actual observation and care¬ 
ful study seem to have established with reasonable 
certainty that corrosion of iron and steel is due to 
an electro-chemical action, and to those of us who 
have studied the subject, the explanation is not a 
very difficult one to understand. 

In order to thoroughly appreciate the importance 
of the electrolytic theory it is essential to bear in 
mind that iron has a certain solution tension, even 
though the iron is chemically pure and the solvent 
is pure water. This solution tension may be modi¬ 
fied by impurities present in the iron or the solvent, 
and again may be exhilarated by certain substances 
that come in contact with the iron. 

Whitney (I) described the subject in a very in¬ 
teresting manner, embodying in his argument the 
interpretation of Nernst concerning the source of 
electro-motive force between a metal and a 

(I) Loc.cit., p. 38. 


—page nineteen 





CORROSION AND PRESERVATION OF IRON AND STEEL 


solution. 11 When a strip of metallic iron is placed in a 
solution of copper sulphate, iron passes into solu¬ 
tion and copper is deposited, this change being of 
course accompanied by a transfer of electrical 
charge from the ions of copper to those of iron. 
Hydrogen acts as a metal and is electrolytically 
classed with copper in relation to iron. If, there¬ 
fore, we immerse a strip of iron in a solution con¬ 
taining hydrogen ions, an exactly similar reaction 
will take place, iron will go into solution, and 
hydrogen will pass from the electrically charged or 
ionic to the atomic or gaseous condition. In such 
a system the solution of the iron, and, therefore, its 
subsequent oxidation, must be accompanied by a 
'precipitation' or setting free of hydrogen. It is 
very well known that solutions of ferrous salts as 
well as freshly precipitated ferrous hydroxide are 
rapidly oxidized by the free oxygen of the air to the 
ferric conditions, so that if the electrolytic theory 
can account for the original solution of the iron the 
explanation of rusting becomes an exceedingly 
simple one." 


—page twenty 





THE ELECTROLYTIC THEORY OF CORROSION 


The application of the electrolytic theory in 
connection with the theory of solution will be 
better understood when we consider that slight 
segregation in the metal, or even unequal stresses 
and strains in the surface will throw the surface out 
of equilibrium, with the result that the solution 
tension will be greater at some points than at others. 
In other words, a point of maximum and a point of 
minimum solution pressure will be established. 
The point of maximum solution pressure will be 
electro-positive to the point of minimum solution 
pressure and a current will flow from one point to 
the other, provided the points are in electrical con¬ 
tact by means of a conducting film. This con¬ 
ducting film may be water, in which case corrosion 
will be very much excited, or conductivity may be 
provided by means of a substance contained in the 
protective coating, or, again, through the inability 
of the protective coating to prevent moisture from 
penetrating through the coating and thus allowing 
moisture to come in direct contact with the steel or 
iron. In the event that a so-called protective 


—page twenty-one 





CORROSION AND PRESERVATION OF IRON AND STEEL 


coating is not entirely free from pores, or contains 
substances capable of conducting electric current, 
it will stimulate rather than prevent corrosion 
simply because the moisture it allows to penetrate 
will cause the iron over which it is applied to pass 
into solution in the electro-positive areas. 

Much light was thrown upon this important sub¬ 
ject by Walker (I), who states as follows. “When 
a piece of iron is placed in ordinary water, exposed 
to the air, it will dissolve or rust. If now there be 
placed in the water with this piece of iron a piece of 
platinum, the solvent or corroding action of the 
water will not be changed. The oxygen is present 
in the solution as before, and the iron ions as they 
separate from the metallic iron are being oxidized 
and precipitated as rust. If now the platinum and 
iron be electrically connected, a marked increase 
in the rate of the solution or corrosion of the iron 
is noticed. No chemical condition has been 
changed; the difference lies in the fact that there 
is now an electrical contact between the iron and 

(I) Jour. Iron and Steel inst. 1909. 


—page twenty-two 






THE ELECTROLYTIC THEORY OF CORROSION 


the platinum, and the platinum furnishes a surface 
on which the hydrogen can deposit, and on which, 
by virtue of its catalysing action, the hydrogen will 
be rapidly oxidized by the dissolved oxygen, and 
thus removed from the sphere of action. ” 

It was believed that owing to the fact that the 
mass metal and" solution are of opposite polarity 
the electrolytic tension became so great that no 
more atoms could escape to the ionic state and that 
therefore the solvent action would cease, but 
Helmholtz described a theory called by him the 
electrolytic double layer which provided infor¬ 
mation of great value. If according to this theory 
(I), there be in the water ions of another metal 
which has a smaller solution pressure than the one 
under consideration, the ion with the less solution 
pressure will pass back to the metallic state, plat¬ 
ing out on the first metal and giving up its charge 
of electricity. At this point the first metal will be 
charged positively, and the solution in the imme¬ 
diate vicinity negative, and there will tend to be 

(I) Corrosion and Preservation of Iron and Steel, Cushman & Gard¬ 
ner, p. 27. 


—page twenty-three 






CORROSION AND PRESERVATION OF IRON AND STEEL 


set up a second electrolytic double layer opposite 
in polarity to the first. The result is, a current of 
electricity flows from the metal to the solution at 
the point where the metal passes into solution, 
through the solution to the metal at the point 
where the ions of the second metal are plating out, 
and back through the first metal to the starting- 
point again. The electrolytic double layers are 
thus destroyed, an electric current passes, and the 
solvent action of the water on the first metal con¬ 
tinues. 

Careful observation tends to support this theory. 
The corrosive action of iron and steel is not arrested 
until the fundamental cause of it is removed, and 
so far as the writer is able to state the influence of 
both water and oxygen upon steel and iron is 
detrimental to its preservation. 

There may be some difference of opinion as to 
the continuation of the solvent action, but that 
iron and steel cannot rust in water unless oxygen 
is present or in oxygen unless water is present is 
pretty well recognized as an established fact. 


—page twenty-four 





THE ELECTROLYTIC THEORY OF CORROSION 


It is of course well to recognize that the solvent 
action of water may be either modified or stimu¬ 
lated depending upon impurities present in the 
solvent. Thus, for instance, waters containing 
carbonic and sulphuric acids will stimulate the action 
of corrosion to a remarkable degree, while any rail¬ 
road bridge engineer will be able to testify that the 
sulphurous gases, liberated through the com¬ 
bustion of coal, play havoc with his steel bridges. 
Rain water seems to have a peculiarly destructive 
action upon steel, which is probably due to the 
carbonic acid present, and mine waters, contain¬ 
ing as a rule, large quantities of sulphur, are very 
violent in their action upon steel. 

Those who have observed the condition of steel 
or iron exposed to sea water or the so-called salt 
water spray, will admit that corrosion of such steel 
is violent and rapid and steelwork thus exposed 
requires positive protection if it is to survive. 

Sea water contains soluble salts which are readily 
and easily ionized, which no doubt accounts for the 
energetic galvanic action and the subsequent pitting 

—page twenty-jive 




CORROSION AND PRESERVATION OF IRON AND STEEL 


and rusting of the steel with which it comes in 
contact. The protection against corrosion of steel 
exposed to sea water is a subject which is receiving 
careful consideration, and will be discussed speci¬ 
fically in another chapter. It is worthy of mention 
here, however, that the electrolytic theory of cor¬ 
rosion is closely related to this particular problem. 

While escaped currents from high potential power 
and light circuits undoubtedly aid in, or aggravate, 
the corrosion of iron, the popular belief that out¬ 
side electrical forces are necessary to produce 
electrolytic action, is not in accordance with facts. 

In “Corrosion and Preservation of Iron and 
Steel” by Cushman and Gardner, the following 
explanation concerning electrolysis is presented:— 
“The phenomenon known as electrolysis takes 
place whenever a current of electricity passes 
through a solution capable of conducting the cur¬ 
rent. Such a solution is known as a conductor of 
the second class to distinguish it from an ordinary 
conductor like a metallic wire, which is of the first 
class. A solution of sugar will not conduct a 

—page twenty-six 




THE ELECTROLYTIC THEORY OF CORROSION 


current of electricity while a solution of salt will 
readily do so. This difference in behavior is 
accounted for by the fact that the salt is dis¬ 
sociated into ions while the sugar is not. A sub¬ 
stance which in solution will conduct electricity is 
known as an electrolyte. The phenomenon of 
electrolysis shows that when a current is passed 
through a solution of an electrolyte, there is a 
mechanical movement of the ions towards the 
electrodes. Thus, if a current is passed through a 
solution of hydrochloric acid the positive hydrogen 
ions will proceed to the negative electrode where 
they will plate out after giving up their electrical 
charges. Having now assumed the atomic or 
gaseous condition, the hydrogen escapes from the 
system in the form of minute bubbles. While this 
action is occurring at the negative pole an equiva¬ 
lent amount of chlorine is being plated out and 
disengaged at the positive pole. 

It is not necessary that an outside or external 
source of electricity should be at work before electro¬ 
lysis can take place. If two strips of dissimilar 


—page twenty-seven 





CORROSION AND PRESERVATION OF IRON AND STEEL 


metal are plunged part way into a solution and 
connected by a wire, or by any other means, across 
the top, a current will flow around the circuit. This 
current is generated at the expense of the more 
electro-positive metal in the couple. The electro¬ 
positive element rapidly shoots off positive ions 
into the solution, thereby leaving itself negatively 
charged so that it invariably appears as the nega¬ 
tive pole in the circuit. Even two steel needles 
from the same package are sufficiently dissimilar 
to show a slight difference of potential when coupled 
in such a way, and one will be protected while the 
other suffers accelerated corrosion. From the 
standpoint of the electrolytic theory all iron and 
steel must be thought of as a composite structure, 
as though, indeed, it was compounded of more or 
less well-consolidated bundles of more or less 
homogeneous needles or units.” 

There seems to be some difference of opinion 
among authorities on the subject of corrosion— 
whether electrolysis is alone responsible for the 
rapid corrosion of modern steel, or whether present 


—page twenty-eight 




THE ELECTROLYTIC THEORY OF CORROSION 


methods of manufacturing steel is contributing its 
share to the ever-increasing corrosion problem. 
H. M. Howe, pleading for modern steel, (I) states 
as follows:—“The fact that steel has come into 
wide use simultaneously with a great increase in 
the sulphurous acid in our city air and of strong 
electric currents in our city ground may well lead 
the practical man, be he hasty or cautious, into 
inferring that the rapid corrosion of today is cer¬ 
tainly due to the new material of today, steel, 
whereas, in fact, it may be wholly due to the new 
conditions of today, sulphurous acid and electro¬ 
lysis. ” 

In discussing corrosion of modern steel, Sang, 
(II), says:—“Carelessness of manufacture, which 
tends to heterogeneousness, is an invitation to 
corrosion, and in itself goes far to explain why 
modern steel, which is tortured into shape at such 
a high speed that the molecules &re not permitted 
to readjust themselves, is said to be more corrodile 
than the metals produced a generation ago; in 

(I) Proc. American Society for Testing Materials, 1906, VII, 155. 

(II) Proc. Eng. Soc. West. Pa., XXIV, 10, p. 511. 


—page twenty-nine 






CORROSION AND PRESERVATION OF IRON AND STEEL 


those days iron and steel were produced in small 
quantities, without the addition of other metals, 
and were rolled slowly and allowed to cool naturally. 
The internal strains due to mechanical treatment 
are not to be confounded with the unevennesses in 
the distribution of the impurities due to segregation 
in cooling; these mechanically induced strains are 
really equivalent to straining the metal beyond the 
elastic limit, which makes it more corrodible. 
Moreover, the tonnage-craze, from which the qual¬ 
ity of product in so many industries is today suffer¬ 
ing, is causing to be placed on the market a great 
mass of material, only a small proportion of which 
is properly inspected, which is not in proper con¬ 
dition to do its work—rails and axles which fail in 
service and steel skeletons for high buildings which 
may carry in them the germs of destruction and 
death. ” 

While it cannot be denied that the hand-wrought 
iron of the past was more resistant to corrosion than 
is our modern steel, yet the present demand for, and 
various uses of, steel prohibits the return to the old 


—page thirty 





THE ELECTROLYTIC THEORY OF CORROSION 


process of hand-wrought iron, and our problem to¬ 
day is to find means to manufacture steel highly 
resistant to corrosion, without reverting back to the 
tedious process of earlier days. 

Civilization cannot go back—it must find 
modern methods for modern problems; it must 
meet conditions,, as they arise, and while striving to 
produce purer, less corrosive steel, it must preserve 
against destruction the countless steel structures 
now in use and those to be erected. 


-page thirty-one 





CORROSION AND PRESERVATION OF IRON AND STEEL 


Chapter III 

Prevention of Corrosion 

When considering the prevention of corrosion of 
iron and steel by means of a protective coating, it 
is essential to bear in mind the now universally 
accepted fact—namely, that corrosion is due to an 
electro-chemical action. 

Furthermore, we must not lose sight of the 
certainty that iron and steel cannot rust unless it 
comes in contact with both water and oxygen. 

It goes without saying, then, that the first re¬ 
quirement of a protective coating should be its 
ability to prevent both moisture and oxygen from 
reaching the surface of the steel or iron. 

The second requirement is that neither the pig¬ 
ments nor the vehicle contain materials which are 
conductors of electric current, or oxygen-carrying 
agents. 

In a paper, (I), “ Conditions that Must Be Met 
in the Ideal Paint for Railway Bridges”, Mr. 

(I) Proc. Third Annual Convention Maintenance of Way Master 
Painters’ Assn, of U. S. & Canada, Nov., 1906. 

—page thirty-two 






PREVENTION OF CORROSION 


Edward Hurst Brown had the following to say: 
“The most insidious enemy of the iron bridge is rust, 
and the primary object of painting is to protect it 
from those elements which cause destruction by 
rust. Rust is caused by the combination of the 
metal with oxygen to form hydrate oxide of iron. 
This oxygen may be obtained from the air, from 
water, or from some other substance which acts as 
a carrier of oxygen or an oxydizing agent—always 
however, in the presence of moisture. Now, one 
of the primary things to be considered in choosing 
a paint for ironwork is that it shall not contain in 
its pigment or vehicle any substance which is 
chemically active in such way as to convey oxygen 
to the iron. For if such a chemically active agent 
be introduced into the paint, sooner or later it will 
promote rather than prevent rust. Of course, so 
long as the oil, in an oil paint, remains intact, it 
envelops the particles of pigment and keeps them 
away from the iron, but in time the oil, which has 
hardened by absorbing oxygen from the air, begins 
to disintegrate by the action of water coming from 


-page thirty-three 





CORROSION AND PRESERVATION OF IRON AND STEEL 

rain, hail, snow, or fog. Moreover, even the 
freshly applied oil is not absolutely impenetrable 
to moisture, as has been shown by numerous experi¬ 
ments, and, however completely the particles of the 
chemically active pigment may be covered by an 
oil film, they will necessarily come in contact with 
moisture—will decompose the water and absorb its 
oxygen, and convey it, together with the hydrogen, 
to the surface of the iron to cause rust. For this 
reason, the ideal paint for a steel or iron bridge 
should not contain a chemically active pigment, nor 
any strongly oxidizing agent in the way of driers. ” 
It will be noted that Mr. Brown makes no men¬ 
tion of the electrolytic theory, but it is plain from 
this article that even before the electrolytic theory 
became understood, authorities realized that pig¬ 
ments incorporated in oil were instrumental in the 
stimulation of corrosion. 

Pigments can stimulate corrosion in three differ¬ 
ent ways, and for convenience sake, it may be well 
to classify the different actions: 

Class 1 . —In this class are included pigments 
which, by virtue of their catalytic action upon the 


—page thirty-four 





PREVENTION OF CORROSION 


oil, cause extreme oxidation of the oil film in which 
they are incorporated. This action, of course, 
shortens the life of the oil, and permits moisture to 
come in contact with the pigments. By decom¬ 
posing the water and absorbing its oxygen, these 
pigments then become active in stimulating cor¬ 
rosion by conveying to the iron or steel both hydro¬ 
gen and oxygen. . 

Class 2. —In this class we have pigments which 
are known to be conductors of electric current. 
The use of such pigments will provide a conducting 
film between the point of maximum and minimum 
solution pressure, with only one result—the form¬ 
ation of auto-electrolysis, commonly known as 
rust. There are also included, pigments (various 
forms of carbon) which, because they so retard the 
drying of linseed oil, demand an excessive amount 
of dryer to be added to the oil, thereby causing the 
oil to oxidize too rapidly, and necessarily shorten 
its usefulness as a water-excluder. 

Class 3. —This class represents pigments which 
are chemically inactive, have no harmful effect 

—page thirty-five 





CORROSION AND PRESERVATION OF IRON AND STEEL 


upon linseed oil, and really are inhibitive in char¬ 
acter, but they have one weakness—they are solu- 
able in water, which makes them undesirable for 
use in structural iron paints. 

It must be remembered, however, that while 
pigments in a paint have a definite mission to per¬ 
form, their proper selection is of no greater import¬ 
ance than is the extreme caution which the pro¬ 
duction of the vehicle demands. 

The writer has stated that the life of a paint is 
dependent upon the life of the oil in which the pig¬ 
ments are ground, and he is not yet ready to retract 
that statement. 

The paint manufacturer who wants to produce 
an honest anti-rust paint must direct all his re¬ 
search to perfecting a combination of pigments 
which will not interfere with the natural life of the 
vehicle, and he must further produce a vehicle 
having maximum durability. 

It is well known that linseed oil, when used alone, 
is not entirely free from pores, and while no other 
oil which can entirely replace linseed oil is available, 


—page thirty-six 





PREVENTION OF CORROSION 

yet a combination of linseed oil and china wood 
oil, properly proportioned, reinforced with selected 
varnish gums, fused together under expert heat 
treatment, produces a vehicle which is much 
superior for use on steel and iron than is a straight 
linseed oil. 

China wood oil is extracted from the nuts and 
seeds of the Chinese tung tree, and when properly 
treated at certain temperatures, produces an oil 
which is well-nigh water-proof. The finished prod¬ 
uct dries with a hard, durable film, and those who 
understand its manipulations consider its use in 
high-grade structural iron paint of incalculable 
value. 

It is certain that in the making of marine and 
water-proof paints, china wood oil is indispensible. 

The average man, not familiar with the paint 
and varnish industry, is apt to consider the pres¬ 
ence in paint of any but linseed oil an adulter¬ 
ation, mainly because he considers that the use of 
such oil is resorted to on account of a cost con¬ 
sideration. Whatever may be the facts regarding 


—page thirty-seven 





CORROSION AND PRESERVATION OF IRON AND STEEL 


the use of some oils, the use of china wood oil never 
cheapens the manufacturing cost of a paint, be¬ 
cause even in its raw state, china wood oil is seldom 
cheaper, and more often, its cost exceeds that of 
linseed oil. When to this, the cost of treatment 
and manipulation is added, it will be seen that its 
use is not suggested because of lower cost, but 
solely because of the added life it gives to the paint. 

To china wood oil is due the great durability and 
water-resisting qualities of some of the best var¬ 
nishes manufactured in the world; in fact, it has 
been said that the advantage which the Chinese 
and Japanese enjoyed in producing paints which 
would dry in damp climates was wholly due to 
their knowledge of the proper manipulation of 
china wood oil. 

The successful preservation of iron and steel 
against corrosion by means of a paint film, is not 
dependent upon any one pigment or upon any one 
oil; it is rather the successful combination of a 
number of pigments, and the perfect fusing of the 
proper oils. 


—page thirty-eight 




PREVENTION OF CORROSION 


Although suitable inhibitive pigments are limited 
there are enough available to enable the honest 
paint manufacturer to utilize them to the fullest 
extent, and a high-grade anti-rust paint can be 
made by those who understand the relative value 
of the right pigments. 

It is not so long ago that graphite and carbon 
paints were considered good protective coatings, 
but thorough investigation led to the conclusion 
that they are stimulative on account of the ease 
with which they conduct electric current. For 
that reason, they should not be permitted to come 
in contact with the steel, and should never be used 
as a priming coat, although, as a second coat, over 
an inhibitive paint, they are of considerable value. 

Red lead, when pure, possesses excellent preser¬ 
vative qualities, but if the red lead is manufactured 
by what is known as the nitrite of soda process, 
there will, unless extreme care is used, remain 
in the red lead a varying percentage of caustic soda. 
Red lead containing caustic soda makes a very poor 
paint, since the caustic soda will saponify the 


—page thirty-nine 





CORROSION AND PRESERVATION OF IRON AND STEEL 


linseed oil, and a short exposure will turn the paint 
into a pinkish white. 

Iron painted with such red lead will corrode 
rapidly, and it is suggested that the engineer who 
pins his faith to red lead, specify a red lead con¬ 
taining a minimum percentage of litharge, and 
absolutely free from caustic soda and nitrite of soda. 

Red lead, if free of caustic soda, while theoret¬ 
ically a good pigment, is liable to fail in practice, 
because of the difficulty connected with its use. 
The chief objection is that it combines readily with 
linseed oil, for which reason it must be used * ‘ freshly 
mixed”; otherwise it becomes hard and cakey and 
unfit for painting purposes. Furthermore, it should 
be mixed in the proportion of not less than 28 lbs. 
(33 lbs. gives the best results) to the gallon of oil. 
The resultant mixture makes a very heavy paint, 
which is difficult to handle, because of its excessive 
weight, and the temptation of the painter to add 
additional thinners is very great, and is generally 
resorted to. 

The fact that in many instances red lead fails to 
give protection is not due to the red lead itself, but 


—page forty 





PREVENTION OF CORROSION 

more often to faulty application and the absence 
of sufficient red lead in the mixture. 

The writer often has observed steel being painted 
with red lead paint containing about 16 lbs. or less 
of red lead to the gallon of oil. Such a mixture 
makes a very poor paint indeed, there not being 
sufficient red lead present to absorb the oil, and 
the resulting film of such a paint is bound to have 
maximum voids, which any engineer knows means 
minimum strength. 

It is refreshing to know that the old-fashioned 
method of mixing by hand so many pounds of dry 
red lead and so many gallons of Linseed Oil is 
rapidly disappearing. 

Anyone at all familiar with the painting of steel 
or iron knows that no hand paddle can thoroughly 
incorporate the pigments into the oil, and even 
those who have no knowledge of painting will 
admit that no hand method can hope to compete 
in efficiency with modern machinery. 

Red Lead is a good pigment, but the amount 
used in structural iron paints should be subject to 


— P a tL e forty-one 





CORROSION AND PRESERVATION OF IRON AND STEEL 


the knowledge and experience of an honest paint 
manufacturer, and when mixed in proper proportion 
with some inert pigment such as magnesium silicate 
or willow charcoal and ground into the oil by means 
of a modern grinding mill, a more superior paint 
will be produced than if only Red Lead were used. 

Red Oxide is a pigment which is little under¬ 
stood, and to specify “Red Oxide” for the shop 
coat means little. We might say that the word 
“Red Oxide” covers a multitude of sins; but while 
all Red Oxides cover the iron very well, not many 
cover it for any length of time. 

The writer has analyzed many so-called Red 
Oxide Paints, and in many cases the ferric Oxide 
(FE 2 0 3 ) did not exceed ten percent (10%) of the 
total pigment, the balance being calcium carbon¬ 
ate, calcium sulphate, silica, or magnesium silicate. 

The market is crowded with Red Oxides. We 
have many varieties of Domestic Red Oxides, and 
since the European War was so successfully termi¬ 
nated, we again have available Spanish and 
Persian Gulf Oxides. 

—page forty-two 





PREVENTION OF CORROSION 


The value of Red Oxide as a pigment for steel or 
iron depends upon the percentage of iron (FE 2 0 3 ) 
it contains. Natural high-grade Oxides usually 
contain from 75% to 85% FE 2 0 3 , and such Oxides 
are valuable pigments in a structural iron paint, 
but they must be used with discretion, and should 
be well ground into the proper vehicle. 

There are obtainable Artificial Oxides of 99% 
purity, but such Oxides are generally made by the 
burning of copperas, and very often contain traces 
of sulphuric acid which have not been eliminated 
during the burning process. It will be obvious 
that Oxides containing sulphuric acid should not 
be used as a pigment for structural iron paints. 

Venetian Reds are often sold under the name of 
Red Oxide. Most Venetian Reds are made by 
calcination of copperas and lime, the reaction form¬ 
ing ferric oxide and calcium sulphate. The per¬ 
centage of (FE 2 0 3 ) in such reds vary from 15% to 
40%, the balance being calcium sulphate. Since 
calcium sulphate is of a very soluable nature and is 
readily ionized in the presence of water, the writer 
considers it a dangerous pigment for steel or iron. 


—page forty-three 





CORROSION AND PRESERVATION OF IRON AND STEEL 


Graphite paints are no longer a factor in con¬ 
nection with priming coats for iron and steel, for it 
is well understood that they are stimulative rather 
than preventative. Graphite conducts electricity 
quite readily, and for that reason alone should not 
be brought in contact with steel or iron, although 
there are other objections well worth mentioning. 

Graphite is a very slow drier and requires exces¬ 
sive amounts of driers to be added. It is a greasy, 
slippery pigment, for which reason it has rather 
large covering capacity, but the resulting film is 
too thin and too porous to afford protection for any 
length of time. Its smooth finish is a serious 
defect, because it makes it poorly adapted for re¬ 
painting, since other paints when applied over 
graphite do not seem to adhere properly. 

Carbon paints are like graphite paints—danger¬ 
ous when used as a priming coat for steel or iron, 
principally because, like graphite, carbon is a good 
conductor of electricity, but in the writer’s opinion 
it has an advantage over graphite when used over 
an inhibitive paint, as it lends itself better to re¬ 
painting. 


—Page forty-four 




PREVENTION OF CORROSION 


Lamp Black, which is made from the combustion 
of oil, is a very pure carbon, often being over 99% 
pure, and while as a second coat over an inhibitive 
paint it has considerable merit, it should not be 
used as a priming coat on iron or steel, since it has 
a high conductivity. 

Bone Black is manufactured by grinding animal 
bones and then burning same in highly heated iron 
retorts. It is considered by the writer an excellent 
inhibitive and is used by him in place of carbon or 
lamp black in the well-known anti-rust paint manu¬ 
factured by his Company. 

Willow Charcoal is a pigment made from the 
charring of willow wood, and besides making a very 
good inhibitive pigment, it is also recommended 
for those who occasionally suffer from indigestion. 
It usually contains traces of alkali, which no doubt 
accounts for the splendid inhibitive qualities it 
possesses. 

Practically all chromate pigments are valuable 
as inhibitors, although care must be taken that 
they are free from acids, and those manufacturers 


— P a l e forty-five 





CORROSION AND PRESERVATION OF IRON AND STEEL 


who have learned the value of chromate pigments 
must be prepared to carefully test them before 
using them. 

There are other pigments which might deserve 
to be specifically mentioned, but since the writer 
is engaged in the manufacture of a high-grade, 
well-known anti-rust paint, he cannot be expected 
to lay bare all the facts which years of study and 
practical experience have brought forth. 

The object of this booklet is not to recommend 
a specific paint, but rather to present to those who 
are interested in the subject a brief outline of the 
facts in connection with the problem civilization 
must solve. 


—Page forty-six 





STIMULATIVE AND INHIBITIVE PIGMENTS 


Chapter IV 

Stimulative and Inhibitive Pigments 

When the writer had become once convinced 
that the electro-chemical explanation of corrosion 
was the correct one, a number of experiments were 
immediately undertaken. 

The first important problem was to determine 
the chemical relation of various pigments hereto¬ 
fore used in structural iron paints. 

During the research work, it was found that cer¬ 
tain pigments when brought in contact with iron 
had a tendency to excite electrical action and stimu¬ 
late corrosion, while other pigments possessed 
ability to inhibit or retard corrosion. 

That certain pigments would inhibit corrosion 
was made clear by Wood (I) as early as 1895, at 
which time he commented on the power of paints 
and pigments containing certain oxidizing agents, 
notably potassium bichromate and lead chromate, 
to form on iron and steel surfaces a thin coating of 

(I) Am. Soc. Mech. Eng. Trans., 1895, 16,671. 


—page forty-seven 





CORROSION AND PRESERVATION OF IRON AND STEEL 


oxide which so effectually protects the metallic 
surfaces from corrosion that after the removal of 
the paint the metal still resists atmospheric effects 
for a long time, as well as the stronger effect of 
immersion in sea-water or acidulated waters and 
sulphurous and other vapors. 

It seemed desirable to demonstrate by a careful 
test whether certain pigments in the presence of 
water would actually stimulate corrosion, and the 
following experiment was undertaken: 

Three sets of fifteen 10-oz. wide neck bottles 
were carefully cleaned and grouped in four sections, 
—two sections of 20 bottles each, one section of 
three bottles and one section of two bottles. 

It was thought advisable to determine whether 
distilled water had any advantage or disadvantage 
over natural water, so in the first and third sections 
distilled water was used, and in the second and 
fourth section water taken from the Allegheny 
River. 

The bottles were numbered as follows:—first sec¬ 
tion 1 to 20; second section 21 to 40; third section 
41 to 43, and fourth section 44 to 45. 


—page forty-eight 





STIMULATIVE AND INHIBITIVE PIGMENTS 


Into each bottle numbered from 1 to 20 was 
placed a measured amount of one of the 20 pig¬ 
ments selected, after which 5 oz. of clear distilled 
water was added. 

Into each bottle numbered from 21 to 40 was 
placed the same amount and kind of pigments as 
in Bottles 1 to 20, after which 5 oz. of water taken 
from the Allegheny River was added. 

Into each bottle numbered 41 to 43 was placed 
5 oz. of clear distilled water, and into each bottle 
numbered 44 to 45 was placed 5 oz. of water taken 
from the Allegheny River. 

Bottles numbered 41, 42, 43, 44 and 45 contained 
no pigment. 

Into each bottle then was placed a piece of steel 
of the same size and cut from one sheet; each piece 
was carefully weighed and numbered from 1 to 45. 

The bottles were then closed with tight-fitting 
corks and sealing wax applied to prevent any 
oxygen from reaching the inside of the bottles, and 
a period of ten weeks was allowed to elapse, during 
which time the bottles were not disturbed, though 
observation was made from time to time. 


— P a S e forty-nine 





CORROSION AND PRESERVATION OF IRON AND STEEL 

It was peculiarly instructive to note that in 
some bottles containing pigments, corrosion of the 
piece of steel was quite apparent in less than five 
days, while in other bottles containing pigment, 
corrosion was not visible through the glass. 

Such observations as were possible through the 
glass did not disclose any material difference in the 
corrosion of the piece of steel in the bottles con¬ 
taining only either distilled or Allegheny River 
water. 

The most convincing evidence, however, was 
supplied when the bottles were opened for final 
examination. 

Three hours after the bottles were opened, the 
pieces of steel were withdrawn, carefully cleaned, 
dried and weighed, the difference in weight of each 
piece of steel from the time they were placed in 
the bottles to the time they were taken out account¬ 
ing for the quantity of steel which was lost through 
corrosion. 

The pieces of steel which were in bottles 11 and 
13 showed almost no loss; those in bottles 31, 32 


—page fiHy 





STIMULATIVE AND INHIBITIVE PIGMENTS 


and 33 were practically free from corrosion. The 
piece of steel in bottle 12 had corroded quite appre¬ 
ciably, and since bottles 11, 12, 13, 31, 32 and 33 
contained chromate pigments, the impression that 
chromate pigments would actually inhibit corro¬ 
sion was well confirmed, with the exception of the 
chromate pigment present in bottle 12. 

A further investigation was conducted, and it 
was found that the cause of the chromate pigment 
in bottle 12 seeming to stimulate rather than pre¬ 
vent corrosion was due to the fact that the process 
of manufacturing chromate pigments determines 
to a large degree whether they are inhibitive or 
stimulative. The impurities present in the chro¬ 
mate pigment in bottle 12 made it stimulative, 
and proved conclusively that great care must be 
used in the selection of chromate pigments when 
used as a pigment in an anti-rust paint. Careful 
analysis should be made before the pigment is 
adopted. 

The steel in bottles 1, 2, 6, 7, 8, 21, 22, 26, 27 and 
28 showed considerable corrosion. These bottles 


—page fifty-one 





CORROSION AND PRESERVATION OF IRON AND STEEL 


contained Lamp Black, Carbon Black, Venetian 
Red, Graphite, Ochre and similar pigments. The 
writer does not hesitate to say that the excessive 
corrosion of the steel in these bottles was directly 
due to the pigments. 

The appearance of the steel in bottles 3, 4, 23 
and 24 proved that the pigments in these bottles 
(Willow Charcoal and Bone Black respectively) 
were inhibitive in character. 

The steel in bottles 5, 9, 10, 14, 15, 16,17, 18,19, 
20, 25, 29, 30, 34, 35, 36, 37, 38, 39 and 40 had cor¬ 
roded to some extent, but in comparison with the 
steel taken out of bottles 41, 42, 43, 44 and 45, 
which, as will be remembered, contained no pig¬ 
ments, it was observed that the corrosion was no 
more severe, so that the conclusion that these pig¬ 
ments neither stimulated nor retarded corrosion 
seemed to be justified. 

It would be difficult to state positively the differ¬ 
ence in action upon the steel of the distilled water 
or the water taken from the Allegheny River. 
The writer believes that corrosion was more severe 


—page fifty-two 





STIMULATIVE AND INHIBITIVE PIGMENTS 


in the bottles containing distilled water, but no 
thorough record was possible. 

It was a singular fact that almost immedi¬ 
ately after the bottles were opened, the water in 
the bottles without pigments and the water in the 
bottles containing stimulative pigments assumed 
a reddish, yellowish color, from which it was de¬ 
ducted that the steel in these bottles had passed 
into solution prior to additional oxygen reaching 
the steel in the bottles. This, in the writer’s 
opinion, proves the contention that certain pig¬ 
ments are stimulative because of their activity in 
decomposing the water, absorbing its oxygen and 
hydrogen, and conveying same to the steel or iron 
to cause rust. 

It is worthy of note to mention that proportion¬ 
ately the steel in the bottles containing only water 
and in those bottles containing stimulative pig¬ 
ments corroded more in the three hours the bottles 
were left open than in the entire period they were 
sealed. It is thus fair to assume that if a supply 
of free oxygen had been available continuously, 
corrosion would have been more severe. 


—page fifty-three 





CORROSION AND PRESERVATION OF IRON AND STEEL 


There was absolutely no change in the steel 
placed in bottles containing chromate pigments, 
with the exception of bottle No. 12, and an explan¬ 
ation for this particular case has been given above. 

The test just described was duplicated a few 
months later, but before the pigments were 
added to the water, all oxygen was removed from 
the inside of the bottles. The general results of 
corrosion, when later on oxygen was introduced, 
were so similar that no material change in deduc¬ 
tions could be recorded. 

A very unique test was recently completed by 
the writer. A wooden tank, 12 x 4 x 4, was filled 
with a salt water solution. Seven (7) strips of 
sheet steel, each painted with a different paint 
made from inhibitive and stimulative pigments, 
were immersed in the solution, connected to each 
other by means of wire, and suspended into the 
solution from wire hooks, which in turn were placed 
on ordinary gas pipe resting on each end of the 
tank. 

The wires connecting the strips were not painted, 
although care was taken to properly paint the edges 


—page fifty-four 





STIMULATIVE AND INHIBITIVE PIGMENTS 


of the holes in the strips of steel. The same pro¬ 
cedure was followed in regard to the wire hooks 
resting on the gas pipe, so that no single spot on 
the strips of steel was unprotected. 

Strips 1, 2 and 3 were painted with a paint con¬ 
taining chromate pigments ground into a “special” 
vehicle consisting of linseed oil, china wood oil and 
varnish gums. 

Strip No. 4 was painted with a chromate pig¬ 
ment paint, the vehicle of which was pure linseed 
oil with the necessary amount of drier. 

Strips 5 and 6 were painted with such pigments 
as former test had shown to be stimulative, ground 
into a vehicle consisting of pure linseed oil and 
drier. 

Strip No. 7 was painted with a combination of 
pigments used on Strips 5 and 6, ground into a 
vehicle consisting of linseed oil, china wood oil, and 
varnish gums. 

The strips were left in the solution for fifteen 
days, after which careful observation was made. 


—page fifty-jive 





CORROSION AND PRESERVATION OF IRON AND STEEL 


Strips 1, 2 and 3 were still perfect. 

Strip No. 4 showed a slight decomposition of the 
paint film. 

Strip No. 5 also showed a slight decomposition 
of the paint film. 

The paint on Strip No. 6 had suffered more than 
that on Strip No. 5; and the paint on Strip No. 7 
was still in excellent condition. 

The strips were again placed into the solution, 
and results recorded each day. 

After twenty days, the paint film on Strips 
4, 5 and 6 began to fail rapidly, and on the twenty- 
fifth day rust became noticeable on Strips 5 and 6. 
Strip No. 4 did not show any rust. Strips 1, 2 and 
3 were at that time still perfect. 

After forty-eight days the film on Strip No. 7 
showed evidence of breaking, and three days later 
rust was observed. 

This test was extended over a period of seventy- 
five days, and the final results as shown on the 


—page fifty-six 





STIMULATIVE AND INHIBITIVE PIGMENTS 


table below are of considerable interest: 


Strip Condition 


1 

Excellent 

Excellent 

Excellent 

Excellent 

2 

Excellent 

Excellent 

Excellent 

Excellent 

3 

Excellent 

Excellent 

Very Good 

Very Good 

4 

Very Good 

Very Good 

Good 

Fair 

5 

Good 

Fair 

Bad 

Very Bad 

6 

Good 

Fair 

Bad 

Very Bad 

7 

Excellent 

Very Good 

Good 

Good 


15 Days 

25 Days 

50 Days 

75 Days 


This test proved: 

1. That the proper chromates ground into the right 
kind of vehicle will retard corrosion. 

2. That the proper chromates ground in linseed oil 
will to a certain extent protect the steel against corro¬ 
sion even after the oil film has ceased to give protection. 

3. That certain pigments will stimulate corrosion, and 
that a pure linseed oil film is not entirely free from pores. 

4. That stimulative pigments cannot set their hostile 
forces to work until the vehicle permits moisture to 
come in contact with the pigments. 

Anyone will appreciate that a seventy-five day 
submersion in a salt-water solution is a very severe 
test for any paint, and the resistance to salt water 
developed by the “Special” vehicle used in this 
test was particularly gratifying to the writer. It 


—page fifty-seven 

















CORROSION AND PRESERVATION OF IRON AND STEEL 


is only fair to add that this “Special” Vehicle is 
the vehicle used in the well-known anti-rust paint 
manufactured by the writer’s company. 

To those who desire to make a rather simple test 
of the inhibitive character of some and the stimu¬ 
lative tendency of other pigments, the following 
experiment is suggested: 

Place a teaspoonful of some of the better known 
pigments, such as graphite, lamp black, yellow 
ochre, red lead, zinc oxide, zinc chromate, lead 
chromate, willow charcoal, bone black, and iron 
oxide in a 4-oz. wide neck bottle, and add from 2 
to 3 ounces of water. Place in the bottles a piece 
of steel or iron (an ordinary nail will do), using care 
that the piece of steel or nail is free from corrosion. 
It is advisable to place the nail or the piece of steel 
in the bottles with the aid of a pair of pliers or 
string, so that the acid of the fingers might not 
cause corrosion. 

Put a tight-fitting cork in the bottle, and allow 
the bottle to remain undisturbed. 

In time you will observe that the steel or nail in 
some bottles will corrode more rapidly than in 


—page fifty-eight 





STIMULATIVE AND INHIBITIVE PIGMENTS 


others, and you will find that the steel or nail in 
some bottles will not corrode at all. 

This simple test will enable anyone to distinguish 
inhibitive from stimulative pigments. 

This test can also be made by eliminating the 
pigments, and by inserting in the bottles pieces of 
steel painted with the different kinds of paint 
recommended for steel and iron. The latter test 
may be advisable, as it will give a comparative test 
of the relative merit of a number of paints on the 
market. 

Recently there has been introduced a test which 
anyone can make, and which, if carefully con¬ 
ducted, will show remarkable results. The purpose 
of this test is to determine the properties of the 
pigments tested in their relation to the formation 
of rust when applied to steel and iron as part of a 
protective coating. The test is carried out as fol¬ 
lows: 

Each pigment selected is mixed to a soft paste 
with water. A sufficient number of Gillette Razor 
Blades (one for each pigment to be tested) are 


—page fifty-nine 





CORROSION AND PRESERVATION OF IRON AND STEEL 


carefully rubbed with fine emery and weighed. One 
blade is then embedded in each paste and wrapped 
with an absorbent paper which will provide perfect 
contact between the paste and the metal. 

This package is now placed in a box lined with 
blotting paper and wetted daily. The package 
should remain in the box for about fifteen to twenty 
days, after which the blade is unwrapped, carefully 
washed free of pigments, and re-weighed. 

The condition of the blade is then noted and the 
loss of weight calculated. Whatever loss of weight 
has taken place has resulted from the formation of 
rust, and of course the greater the loss the greater 
the amount of rust which was formed. 

This test will conclusively show that some pig¬ 
ments cause a greater loss than others, and fairly 
correct data concerning the stimulative and inhibi- 
tive qualities of pigments can thus be obtained. 


—page sixty 





THE LAW OF MAXIMUM AND MINIMUM VOIDS 


Chapter V 

The Law of Maximum and Minimum Voids 

A paint designed to protect wood will stand 
guard against decay just so long as it prevents 
moisture from reaching the surface over which the 
paint is applied. 

In recent years, much attention has been given 
to the so-called reinforcing of linseed oil when used 
as a vehicle for house paint, and splendid results 
have been obtained. 

The modern paint manufacturer has in view only 
one object, and that is to increase the life of his prod¬ 
uct ; and since the veil of secrecy (which for many 
years was in vogue in the paint and varnish in¬ 
dustry) has been allowed to be lifted, much re¬ 
search work has been conducted on what might be 
termed a co-operative scale. 

Co-operation is conductive of progress, and so 
we have today a pretty thorough understanding of 
the underlying principles of modern paint-making. 

Like any industry, the paint and varnish in¬ 
dustry has its pioneers, and due to their efforts, 


—page sixty-one 





CORROSION AND PRESERVATION OF IRON AND STEEL 


greater progress will undoubtedly be made, but it 
will be admitted that enough information is avail¬ 
able to enable the reputable manufacturer of house 
paints to furnish a product of real merit. 

It is unfortunate that the manufacture of struc¬ 
tural iron paints is not so generally understood. 
At least, one is compelled to reach that conclusion 
when the different kinds of structural iron paints 
offered for sale are subjected to a close examination. 
While individual efforts have been directed to the 
perfection of a real anti-rust paint, no general 
revival has taken place, and today graphite paints 
are recommended pretty much like they were be¬ 
fore it was discovered that they are stimulative. 
The same holds true insofar as carbon and similar 
paints are concerned. 

Since moisture is always the deciding factor in 
either the decay of wood or the corrosion of iron 
and steel, it must be obvious that all care must be 
directed to prevent moisture from reaching the 
surface. 

A linseed oil vehicle can be made more water¬ 
proof by the addition of certain varnish gums, 


—page sixty-two 





THE LAW OF MAXIMUM AND MINIMUM VOIDS 


which however must be added under conditions 
which should be thoroughly understood and with 
extreme care and discretion. The oil must be 
heated to the proper degree and the gums incor¬ 
porated at the right time, and the degree of heat 
necessary can only be determined through careful 
and tedious experimenting. Those of us who have 
given this subject attention know the efforts re¬ 
quired and are not unmindful of the caution which 
must be exercised. 

It is not fair to expect a certain part of a com¬ 
bination to stand all the strain or to bear the entire 
burden; consequently, no one should expect the 
vehicle in a structural iron paint to shoulder all the 
responsibility. A man should not, in fact, does 
not expect his wife to be the housekeeper and the 
breadwinner (although some of us have tried to get 
away with it), because, if the wife was willing or 
able to assume both jobs (and housekeeping really 
is a job) she would not need, or desire, to have 
one of us poor men as a partner; and for the same 
reason, if the vehicle in a paint is to do the entire 

—page sixty-three 





CORROSION AND PRESERVATION OF IRON AND STEEL 


job, the rest of the combination (pigments) are 
not required. 

Pigments, however, are needed, and their proper 
selection for different paints constitutes an impor¬ 
tant part of modern paint-making. 

That certain pigments, by virtue of their cata¬ 
lytic action upon the oil, shorten the life of the oil, 
is now well recognized; hence, such a pigment must 
either be eliminated altogether, or its harmful effect 
should be counteracted with some other pigment. 
The presence thus of more than one pigment is 
often desirable from a chemical point of view, but 
from a physical point of view, it is absolutely 
essential. 

Anyone with but a superficial knowledge of 
physics, will understand that the mixing with a 
liquid of one pigment (the particles of which are all 
of the same size) will produce a mass or film having 
maximum voids, and maximum voids means mini¬ 
mum strength. 

In a paint film, the law of maximum and mini¬ 
mum voids is very important, because the more 


—page sixty-four 





THE LAW OF MAXIMUM AND MINIMUM VOIDS 

voids in the film, the more weak spots will be open 
to the attack of moisture and other injurious 
elements. 

Furthermore, the combination of several correct 
pigments assist materially in making the paint film 
resistant to moisture, and by so doing, these pig¬ 
ments are instrumental in increasing the life of the 
paint. 

Cement is a very necessary ingrediment in con¬ 
crete up to a certain quantity, but the more 
we exceed the necessary quantity, the more will we 
weaken the tensile strength of the concrete. 
So it is with a paint film—a combination of pig¬ 
ments will outlast a single pigment, no matter how 
excellent this one pigment may be. 

No one will deny that white lead is a splendid 
pigment, but anyone interested can easily satisfy 
himself that pure white lead and linseed oil cannot 
successfully compete in lasting qualities against 
a mixture of white lead, zinc oxide and a small per¬ 
centage of either barium sulphate, silica, or magne¬ 
sium silicate and linseed oil. 


—page sixty-five 





CORROSION AND PRESERVATION OF IRON AND STEEL 

Paint, as well as cement, requires reinforcing. 
In concrete we use sand and gravel; in paints, be¬ 
sides zinc oxides, there are many so-called inert 
pigments which are indispensible, and expert 
knowledge of these pigments on the part of the 
paint manufacturer will enable him to deliver an 
article of superior merit. 

Structural iron paints should never consist of one 
pigment, mainly because such a paint film would 
have maximum voids, and moisture would soon 
destroy its usefulness. 

An extensive test conducted by the writer, which 
covered a period of years, demonstrated con¬ 
clusively that no single pigment paint can compare 
in efficiency with a properly balanced paint con¬ 
taining from three to five pigments, and those 
paints containing varying percentage of chromate 
pigments proved most effective in the prevention 
of corrosion. 


—page sixty-six 





PROTECTION AGAINST THE ACTION OF SEA WATER 


Chapter VI 

Protection Against the Action of Sea Water 

The problem of protecting against corrosion steel 
work exposed to sea water is of such great im¬ 
portance that the writer feels it necessary to include 
a special chapter. 

The soluble salts present in sea water will pene¬ 
trate through ordinary paint films in a very short 
time, and if such paints contain pigments which 
are stimulative in nature, galvanic action will pro¬ 
ceed at an alarming rate. It is not difficult to 
account for this, since these soluble salts will not 
only dissolve the paint film but will readily ionize, 
thereby causing, with the aid of such pigments, 
electrical charges to flow from the point of maxi¬ 
mum to the point of minimum solution pressure. 
A solution of salt will readily conduct a current of 
electricity, which is accounted for by the fact that 
the salt is dissociated into ions. 

Inhibitive pigments therefore should always be 
present in a paint designed to withstand the action 
of sea water. 


—page sixty-seven 




CORROSION AND PRESERVATION OF IRON AND STEEL 


While obviously the pigments constitute a very 
important factor, the selection of the vehicle is of 
even greater consequence. Straight pure Linseed 
Oil will not fill the bill,—first, because such a film 
would not be free from pores, and, second, because 
its resistance to sea water is not very great. This 
statement should not be interpreted as a reflection 
upon Linseed Oil, because sea water has been 
known to penetrate the hardest paint film. It is 
the writer’s opinion that for many purposes, Lin¬ 
seed Oil stands in a class by itself and cannot be 
replaced. It is only fair, however, to recognize its 
few weaknesses while crediting it with many excel¬ 
lent qualities. 

The action of sea water is extraordinary and the 
protective coating should therefore be no less extra¬ 
ordinary. 

All possible research should, and in individual 
cases, has been directed to the perfection of a vehicle 
resistant to the action of the soluble salts which 
constitute a part of sea water. Water-exclusing 
properties should be its predominating virtue, and 


-page sixty-eight 





PROTECTION AGAINST THE ACTION OF SEA WATER 


special attention should be directed to making the 
vehicle impervious to the soluble salts. 

Expert manipulation of linseed oil, china wood 
oil and certain varnish gums will make the produc¬ 
tion of such a vehicle possible, and it is a matter of 
record that a vehicle perfected by the writer showed 
remarkable resistance to sea water. 

One thing is certain—the electrolytic theory is 
applicable in no case so convincingly as it is in the 
corrosion of iron and steel subject to the attack of 
sea water. 


—page sixty-nine 





CORROSION AND PRESERVATION OF IRON AND STEEL 


Chapter VII 

Concrete as a Protector Against Corrosion 

The question whether structural steel ultimately 
to be imbedded in concrete should be protected 
against corrosion by means of a paint film is a much 
debated one. 

Many engineers, basing their opinion upon past 
experience, claim that concrete is a perfect insula¬ 
tor against corrosion, and under many circum¬ 
stances, the writer agrees with that view. 

It is a well known fact that iron does not rust in 
a highly alkaline solution, although rusting pro¬ 
ceeds dangerously when the alkalinity is not high 
enough. Before corrosion can proceed, however, it 
is necessary that oxygen comes in contact with the 
steel, and it seems reasonable to assume therefore 
that steel imbedded in concrete, provided oxygen 
cannot reach the surface, is effectively protected 
against corrosion by the concrete or cement. 

There, most generally, is sufficient alkali in the 
concrete to afford protection, and the writer has 


—page seventy 





CONCRETE AS A PROTECTOR AGAINST CORROSION 

seen many examples of steel imbedded in concrete 
for many years, which upon removal of the con¬ 
crete was in perfect condition. 

There usually are spots where corrosion is very 
severe, but these spots are localized and generally 
occur only where the steel rises above the grade 
line, at a joint, or where crevices in the concrete 
allowed oxygen and moisture to reach the steel. 

Such experiments as the writer has made, and 
such observation as has come to his attention would 
seem to justify him in stating that where the struc¬ 
tural steel is comparatively free from corrosion at 
the time the concrete is poured, and where the 
concrete is of sufficient density to prevent oxygen 
from reaching the steel, and provided that a perfect 
bond between the steel and the concrete is assured 
no fear for corrosion need to be entertained. 

It must be obvious to anyone that a bond 
between the steel and the concrete is essential. 
Concrete will adhere perfectly to steel when com¬ 
paratively free from corrosion, but if corrosion is 
appreciable at the time the concrete is applied, a 


—page seventy-one 





CORROSION AND PRESERVATION OF IRON AND STEEL 

perfect bond will not be obtained, and corrosion 
might proceed, with the added danger that it is 
likely to cause the concrete to crack, which, if so, 
would increase the corrosion because the porous 
or cracked concrete would permit water to find its 
way to the steel. 

Delays not anticipated at the time the work was 
undertaken might necessitate lengthy postpone¬ 
ments, during which time the unprotected steel 
might be exposed for a long time, and of course 
corrosion would be very severe, and such steel 
would really be unfit to receive concrete. 

The writer knows of one case where approxi¬ 
mately 3000 tons of steel were allowed to remain 
at the building site for more than two years before 
erection could proceed. At the time the steel was 
ordered everything pointed to immediate erection 
and subsequent application of concrete, conse¬ 
quently the steel was ordered unpainted. When it 
was possible to resume work, the steel was in such 
terrible condition due to corrosion that it was con¬ 
sidered hopelessly deficient for the purpose origi¬ 
nally intended. The only way which remained open 


—page seventy-two 





CONCRETE AS A PROTECTOR AGAINST CORROSION 


was to thoroughly clean and paint the steel, which 
was subsequently done, but at a cost which ex¬ 
ceeded by many thousand dollars the nominal 
charge for which that same steel could have been 
painted in the shop prior to shipment. 

Such an occurrence is by no means uncommon, 
and it would therefore seem that the Engineer in 
charge of the work is best qualified to determine 
whether steel to be embedded in concrete should or 
should not be painted in the shop prior to shipment. 

If the steel can be imbedded in concrete before 
excessive corrosion takes place, painting is not 
essential, but since the application of a shop coat 
can be secured at a cost insignificant compared to 
the benefits derived, it seems that prudence would 
suggest a course of certainty rather than that of 
uncertainty. 

Careful consideration, however, should be given 
to the character of the paint best suited for the 
purpose. 

Linseed oil paints are of no use; in fact, their 
use would be detrimental, since linseed oil is a 
saponifiable oil. The writer has on many occasions 


—page seventy-three 





CORROSION AND PRESERVATION OF IRON AND STEEL 


demonstrated that the alkali in the cement will 
saponify and destroy the linseed oil, by virtue of 
which a bond between the concrete and the steel is 
prevented. 

A very interesting experience of a well-known 
Construction Engineer related by him to the writer 
conclusively proves the accuracy of the above 
statement, and while the case in question may be 
an unusual one, the evidence secured was so con¬ 
vincing that the writer cannot forego the pleasure 
of imparting it to his readers. 

Some years ago this Engineer was in charge of 
the erection of a large warehouse. This warehouse 
was designed for the storing of heavy materials, 
which necessitated the use of very heavy beams 
for the floors, on which the shop paint was Red 
Lead in Oil. The building had concrete floors, 
and the floor beams were encased in concrete. 

Some weeks after the concreting had been done 
it was discovered that a mistake had been made in 
the spacing of the floor beams, and they had to be 
taken out in order to correct the error. The job 


—page seventy-four 







CONCRETE AS A PROTECTOR AGAINST CORROSION 


of getting the floor beams out of the mass of con¬ 
crete was anticipated with a great deal of anxiety, 
because it was thought that the floor consisted of 
a solid mass of concrete and steel. Imagine, there¬ 
fore, the surprise of everybody when it was found 
that the beams could be taken out of the concrete 
in the same manner that one could withdraw a 
warm knife out of a mass of butter. The beams 
were literally pulled out of the concrete, since there 
wasn’t the slightest resemblance of a bond between 
the floor beams and the concrete. 

This incident certainly substantiated in unmis¬ 
takable terms the writer’s claim that a linseed oil 
paint is totally unfit for steel which is to be imbed¬ 
ded in concrete. 

Paint designated for this purpose should contain 
only non-saponifiable oils, so that no chemical re¬ 
action takes place when it comes in contact with 
the concrete; it must also provide a bond between 
the steel and the concrete, and dry with a water¬ 
proof film. China wood oil can be successfully 
employed and the selection of proper pigments can 
make such a paint highly rust resisting. 


—page seventy-five 





DESIGNED AND PRINTED BY 
WILLIAM G. JOHNSTON COMPANY 
PITTSBURGH • PENNSYLVANIA 





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